Chap. II. THE EMYDOID.E. 355 



toes of the hind feet are at or very near the sliiekl where the edges of the car- 

 apace and plastron meet, so that the entire surface on each side hetween the fore 

 and hind leg is protected hy the bridge which connects the lower flattened sur- 

 face of the plastron witli the outer edge of the carapace. Thus the retracted 

 limbs and the tail are placed nearly horizontally between the projecting free edges 

 of the carapace and plastron ; but when the plastron is hinged, its ends are raised, 

 and they are pushed further upward and inward. 



The size varies exceedingly in this family ; it is larger than in the Cinos- 

 ternoidiT?, and smaller than in the Testudinina. The smallest known species, Emys 

 Miihlenbergii, is about four inches long ; the largest, Ptychemys rugosa and conciiina, 

 are about fifteen inches long. The largest species are among the most acjuatic. 



None of the species catch active prey, or are in any way ferocious ; they 

 are indeed entirely harmless, and only when hard pressed defend themselves by 

 biting; they do not, however, snap repeatedly with the head against their assailants, 

 as the Cinosternoidai do. Their food is both vegetable and animal ; the latter they 

 tear with the jaws, holding it down, when necessary, with the fore feet. In cap- 

 tivity, they are very fond of worms, and green leaves, and berries ; the more ter- 

 restrial species feed upon grass. 



The Emydoida^, like all other Turtles, lay their eggs upon dry land, in holes 

 which they dig themselves with their hind legs. The number of eggs they deposit 

 at one time varies more, with different species, than in any other family. The 

 more terrestrial species lay the fewest eggs, from two to three, to five or seven ; 

 while the aquatic species lay many more, from ten to fifteen, to twenty, thirty, 

 and even more. The form of the eggs is that of a more or less elongated 

 ellipse; the shell is never brittle, but rather flexible, and less calcareous than in 

 most other families. 



The minor differences of form, observed among the Emydoidte, suggest the fol- 

 lowing subdivisions, which appear to bear the character of sub-families ; but, until I 

 have examined a greater number of the species found in South America and in 

 the Old World, I do not venture to insist upon the accuracy of their limits. 



1. Nectemydoid.e. The body is rather flat. The bridge connecting the plas- 

 tron and cax-apace is wide, but flat. The hind legs are stouter than the fore legs, 

 and provided with a broud web, extending beyond the articulation of the nail 

 joint. The representatives of this group are the largest and the most aquatic of 

 the whole family. 



2. Deirochelyoid.e. The body is higher and more elongated ; the bridge con- 

 necting the plastron and carapace is not only wide, I)ut at the same time high. 

 The plastron itself is narrower than in the preceding tribe. The neck is remark- 

 ably long and snake-like, and recalls that of the Chelodinaj among the Pleuroderes. 

 The feet are webbed. 



